1. Field of the Invention
The present invention relates in general to an air valve for an air intake manifold, and more particularly to a low-leakage air valve for a variable air intake system for a plastic manifold assembly.
2. Description of the Related Art
In some internal combustion systems, it is desirable to vary an air intake runner length for optimizing engine performance during operation.
Plastic air intake manifolds with active runner systems use an air valve to shorten the air flow path at high rotations per minute (RPM) to optimize engine torque. Any leakage in these valves reduces torque. Conventional aluminum manifolds use precision-machined sealing surfaces on the butterfly plate and its mating manifold surface. Plastic manifolds use molded in finishes and have dimensional tolerances far greater than machined finishes. As such, problems can arise with leakage.
Port throttle valves are typically employed to regulate air flow to an internal combustion engine. They are also referred to as a "butterfly" valve which includes a body with a valve plate that extends across a throat or port on a rotatable shaft. A fully sealing valve is difficult to achieve because of clearances required for assembly of the many components in such air intake systems and the close tolerances.
One approach is to eliminate butterfly valves as taught in U.S. Pat. No. 5,454,357. This patent describes a sliding port valve for an internal combustion engine which is intended as an alternative to a butterfly valve in the intake system for the control of intake air.
Another approach is to rubber coat a plastic butterfly valve to make up for reduced accuracy of plastic parts. This type of valve still lacks improved sealing characteristics due to the fact that while vacuum assists the seal on one side of the butterfly valve by drawing the flexible lip down which increases the sealing force, it has a reverse effect on the opposite side where it tends to provide a less effective seal as the vacuum decreases the sealing force. Also, the shaft seal ordinarily employs a "bell-shaped" lip that compresses against the side walls. Vacuum leaks past the initial seal into the bell where it then aids the seal by increasing the sealing force on the atmospheric side of the bell.
There still exists a need for an improved low-leakage air valve for an air intake manifold. Such a valve would offer the advantages of a butterfly valve including the ability to have a rubber coating or an elastomeric outer seal and still effectively provide an increased sealing force particularly when applied to plastic parts.